(1) Field of the Invention
The invention relates to a device for slit radiography comprising an X-ray source; a slit-shaped diaphragm which is placed in front of the X-ray source and forms a fan-shaped X-ray beam during operation with which a body to be examined can at least partially be scanned for the formation of an X-ray shadow image of the scanned part of the body on an X-ray detector placed behind the body; a control signal generator which feeds a signal representing the instantaneous transmission of the body to control means during operation per sector of the fan-shaped X-ray beam; controllable attenuating elements which interact with the slit diaphragm and can influence the fan-shaped X-ray beam per sector under the control of control signals provided by the control means.
(2) Description of the Invention
A device cf this type is known from Dutch Patent Application 8,400,845. According to the technique known from Dutch Patent Application 8,400,845, the quantity of X-rays transmitted at any time by the slit diaphragm is regulated by using attenuating elements which are placed at or in the slit of the slit diaphragm, can each influence one sector of the fan-shaped X-ray beam and are controlled depending on the attenuation occurring in the associated sector and caused by the body to be examined, in a manner such that the attenuating elements reach into the X-ray beam to a greater or lesser extent. If the attenuation caused by the irradiated body in a specific sector at a specific instant is high the attenuating element belonging to this sector is moved entirely or considerably out of the X-ray beam. If, on the other hand, the attenuation caused by the body in a specific sector at a specific instant is low the associated attenuating element is brought further into the X-ray beam.
It is an advantage of this technique that equalized radiographs, that is radiographs having been exposed correctly both in the light parts and in the dark parts, can be obtained therewith. Accordingly, if, for example, an image is taken in this manner of the upper part of a patient's body the radiologist can find sufficient information, in one and the same image, about both the lungs and the abdomen of the patient whereas two different images have so far been necessary to obtain the same information.
The known technique has the drawback that in principle X-rays of the same hardness are used for both the transparent parts and for opaque parts of the patient, whereas a relatively greater X-ray hardness is desired for the opaque parts than for the transparent parts in order to obtain better exposure in the opaque parts and better contrast of the X-ray shadow image to be formed in the transparent parts.
The invention therefore aims at improving the known technique and generally at providing an effective device for making equalized radiographs.